= nifty, eerie patterns. Towards the end, the shapes get more complicated and start shifting rapidly between ordered forms. For a second I thought the devil's face might appear.
[Added -- commentary from my father: This is standard solution of wave equation in rectangular cordinates. We used to try to make Bessel functions with coffee cups when in graduate school seminars; this is solution to wave equation in cylindrical coordinates. In that case, the wall is node, as it does not move , so it restricted the possible orders.
physics is fun!